In order to keep optical fibers in the form of optical glass fibers free from outside influences, optical fibers are generally protected by a jacket. A simple possibility to protect optical fibers in the form of glass fibers against outside influences consists of providing the optical fiber with a coating and immediately applying a firm protective jacket made of a suitable plastic over the coating of the optical fiber. Such an arrangement is commonly designated as an insulated core or filled core. Such a core construction distinguishes itself by a substantial decrease of the outer diameter of the core in contrast to a loose tube.
Especially for the installation and connectorization it is necessary to remove the core jacket of an insulated core from the optical fiber. To make it easier to remove a PVC core jacket, which contains polyvinylchloride, from the coating of an optical fiber, it is usual to place a Teflon layer (so-called TB-2 coating) between the core jacket and the coating of the optical fiber as a separating layer. Thus a user can strip the core jacket of an insulated core over a greater length in one step.
An optical insulated core thus constructed has, however, certain disadvantages. An optical insulated core with a TB-2 layer is comparatively more expensive to produce, especially the application of the different layers is comparatively costly. During application of the layers in one work process, the danger exists for an uneven layer thickness and formation of kinks in the Teflon due to abrasion in the extruder tool. Additionally, due to voids where there is no Teflon, localized attenuation peaks can occur. Furthermore, generally only a limited pay-off speed is possible during the extrusion process. With a 2-step extrusion process, where the Teflon layer is applied first followed by the PVC core jacket, additional investment costs are incurred due to the necessary expansion of the extrusion lines. Handling problems can also be created, since the Teflon layer is commonly formed as a 3-component mixture and the components contain hazardous elements.